For many years, the lower-priced end of the pencil market has been dominated by conventional wooden pencils with mechanical pencils being unable to secure but a minor portion of the market. A number of factors have contributed to this division of market share, most importantly, the relative expense of the mechanical pencils which have been made available requiring that they be regarded as nondisposable items. Many attempts have been made to develop a simplified mechanical pencil which can compete with the less expensive wood pencils. Such pencil would overcome the disadvantages of the need to sharpen the point and the fact that the entire length of the wooden pencil is not usable. Although some of the designs for disposable mechanical pencils in the prior art would appear to be less expensive to manufacture than conventional mechanical pencils, they are still generally much more expensive than the common wooden pencil and hence have not been able to acquire a significant share of that market.
Among such designs is that shown in U.S. Pat. No. 3,771,882, which employs a longitudinally movable finger projecting from the side of the pencil barrel to advance the lead as it is consumed during use.
The design shown in U.S. Pat. No. 3,806,262 attempts to simplify a mechanical pencil design by eliminating the need for finger-actuated advancement of the lead, relying instead on a translating member mounted within a flexible tubular pencil barrel to translate deformation forces applied to the pencil barrel by the fingers to axially advance the lead as needed.
The mechanical pencil described in U.S. Pat. No. 4,136,980 attempts to simplify mechanical pencil construction in a manner in which the back and forth movements of the pencil lead are controlled by a lead carrier having a spiral guide travelling along the spiral grooves formed on the inside of the pencil barrel and moving in response to manual rotation of the cap which holds one end of the supporting member.
Most of the mechanical pencils which have been commercialized successfully have relied upon the use of a helical feed mechanism to advance or retract the lead in response to the relative rotation of the body of the pencil and either its tip or cap. Such pencils are exemplified in U.S. Pat. Nos. 2,161,889; 2,356,509; 2,563,128; and 2,866,438.
While it has generally been felt by those skilled in the art that a helical advance-retract mechanism could not be produced economically enough for use in a disposble mechanical pencil, there has now been discovered a construction which may be manufactured in large volume at a low enough price to compete more effectively with the conventional wooden pencil.